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Animal Navigation Introduction One of the most remarkable features of many non-human animal species is their ability to navigate over vast distances. Examples of this animal-Olympic ability include homing pigeons which can cover over 600 miles in one day (a feat Virgin rail can only dream about!) and the albatross that migrates over 4000 miles. The Arctic tern accomplishes a particularly impressive feat, although it does leave you wondering what the point is; it spends 2 weeks at the North Pole, a few weeks at the South Pole and the rest of the year flying between the two! Navigation over such vast differences may be for one of two main reasons; homing or for the purposes of migration. Questions on this topic will not specify which. Typical wording would be ‘discuss research studies into homing and/or migration in non-human species.’ This is fortunate because the two are difficult to disentangle. Surely if an animal migrates then on the return journey it is using similar skills and techniques in order to get home! However, I shall briefly look at the reasons for homing and migration before considering the techniques that may be used. Homing The texts say little about this other than stating the obvious, i.e. that it is the ability to find ones way home! There are clear advantages of being able to do this. If a species has to go out looking for food or mates then it needs to be able to find its way back to its burrow, nest etc. where presumably it is safer. If young are involved then it is essential that food can be taken back for them etc. The most famous species for its homing ability has to be the ‘homing pigeon’ but others include the salmon, purple martin and African antelope. Migration The reasons for this are not always so obvious but the texts have far more to say on the issue. Migration refers to the seasonal movement of some species which appears to be triggered by environmental factors such as temperature. Remember that migration is seen as a circannual rhythm. There are several advantages to migrating including warmer weather and avoiding severely cold weather at the poles, new feeding grounds or watering holes, possibility of finding new mates or sometimes avoiding predators. All of these are clearly advantageous to a species and increase its chances of survival or reproduction. However, migration comes at a cost. Vast amounts of energy can be consumed and there may be many dangers, such as predators, on the way. Fisher (1979) reported the death of at least 3,200 birds in one night in Illinois. The birds had flown into radio masts and similar tall structures!
Birds We normally associate migration with bird species. It is unusual for birds to migrate in one stage, preferring to break the journey down into smaller stages en route. Migratory journeys by birds appear to be a combination of innate and learned skills and this is best illustrated using the example of Perdeck’s starlings (1958). The starlings migrate in autumn from their breeding grounds in Russia to northern France, a south westerly journey. Perdeck intercepted some of the starlings en route in the Netherlands and took them south to Switzerland. Some birds were experienced others novices on their first migration. Perdeck found that when the birds were released to continue their journey that the young birds continued flying in a south westerly direction which brought them out in northern Spain, well south of where they should have been. However, the experienced birds (no rude comments), with the benefit of past migrations behind them, were able to adjust for the displacement and still find their way to north France. Perdeck concluded that the young birds were relying on innate skills whilst the mature birds were able to combine innate skills with learning from previous experience. Helbig (1991) in a bizarre but ingenious experiment showed the importance of innate factors. He took two related species of black cap, one of which migrated south east and the other south west. When these were cross bred their offspring, (you guessed it) flew south! Migration in the European stork also appears to be innate. Regardless of where the storks originate they all migrate to the same area of north Africa. Storks in Eastern Europe set out in an easterly direction and go via the Middle East. Storks in Western Europe set out in a south westerly direction and fly across the Mediterranean at Gibralter. Schuz (1971) took eggs of the east European species and transferred them to nests in the west. When they migrated they flew in an easterly direction just like their biological parents.
"Herds of wildebeest sweeping majestically across the plain" Basil |Fawlty 1979
Fish and sea creatures Just as birds may use air currents such as thermals to help migrate then many sea species use underwater currents such as the Gulf Stream to cover vast distances. The loggerhead turtle is one such example. Navigation beneath the sea can be more problematic, for example it is more difficult to use sun, moon and stars. Some research suggests that it may be possible, for example loggerhead turtles in captivity swim towards light sources, but generally it is assumed that their vision is not good enough to make this a reliable method of navigation. Salmon are probably the fish most famed for its homing instinct. Here smell seems to play an important role in finding natal streams (streams where they were born). More detail about this later.
So having considered two reasons for why a species may need to navigate over long distances we will now consider how they achieve this feat. This is the most likely area to be examined!
Methods of navigation The simplest method of navigation is leaving a trail that can be retraced, like Daedulus in the Minotaur’s Labrynth (for classical scholars). The loris (a type of lemur apparently), uses ‘urine washing’ in which they pee on their hands and then rub the urine onto their feet to leave a scent trail. Try it the next time you’re out! Slightly more complex is piloting in which landmarks are remembered en route. These may be visual or olfactory but this method is only useful over short distances. Navigation by direction is the most complex and involves the use of sun, moon, stars and magnetic fields to orientate yourself in relation to your destination. In the following section I shall only consider the last two options.
Piloting or navigation by location can use either visual landmarks or smells. Landmarks Tinbergen & Kruyt (1938). If you’ve already revised animal memory you’ll be familiar with this one. This is still a classic experiment and needs to be treated as a key study. The researchers placed pine cones outside the nests of digger wasps, a species that lives in the ground. When the wasps leave the nest they orientate themselves by circling over the entrance to the nest and noting the position of landmarks, in this case the strategically placed pine cones. The researchers then move the cones a few metres away but keeping the same pattern. On their return the wasps still try to locate the entrance to the nest in the centre of the pine cones. As mentioned in memory notes, the researchers ruled out the possibility of smell being used by using a combination of scented pine cones and scented plates. Extension material but good for evaluation marks (AO2): Beusekom (1948) carried out a variation on the study placing pine cones in a circle around the entrance to the nest. When the cones were moved they were placed either in a circle, an ellipse or a square. They found that the wasps would try to find the entrance in the circle and the ellipse (a similar shape) but not in the square. In behaviourist terms the wasps had generalised the initial learning to an ellipse (just as Little Albert generalised from white rabbit to cotton wool etc), however they were able to discriminate between circle and square. Clearly landmarks are of limited use and are only suitable for navigation over short distances. It was once thought that racing or homing pigeons could find their way home by following landmarks remembered when they were being transported on their outward journey. Walcott & Schmidt-Koenig (1973) showed that this could not be the case by anaesthetising the birds during transportation! It is now thought that pigeons use a variety of methods for long distance navigation and only rely on landmarks for the last bit of the journey and locating the precise loft. (See notes on cognitive maps in ‘animal memory’ if you require further evidence).
Cartwright & Collett (1983) trained gerbils to find sunflower seeds and bees to find sugar solution. They arranged the food so that it was always a fixed distance and direction from a 40cm high cylinder. If the position of the cylinder was moved then this confused the creatures who would search in the wrong place suggesting:
However, the two species seemed to be using different techniques. When the height of the cylinder was altered the bees were confused. The researchers concluded that bees were using the size of the retinal image to locate position. However, height of the cylinder made no difference to the gerbils’ ability to find the food. Cartwright & Collett believed that the gerbils were using dead reckoning.
Dead reckoning This is the ability to know your location in respect to the target location in terms of the distance and direction moved away from it. Even when animals have taken a circuitous route away from the location they can still take the shortest route back. This is like you going to Leicester via Northampton and Coventry but coming back straight down the A6!
Olfactory maps As already mentioned the salmon appears to navigate its final stage of the journey home using smell. Much of the research on smell has been carried out by the Italian Papi. He believes pigeons build up a map of their location based on smell (olfactory map). Pigeons have been denied their sense of smell by a variety of methods, e.g. cutting their olfactory nerve, local anaesthetic or bunging wax up their nostrils! This does appear to disorientate them. However, it could be the pain and discomfort of the methods used that causes the problem. Strangely this disorientation only seems to occurr in Italy. It has been suggested that pigeons here rely on smell more because they tend to be kept in lofts high up on roof tops. In Frankfurt birds kept at ground level and deprived of smell are able to home okay. This suggests that the way birds are reared does affect their navigational abilities.
In more ethical follow up studies the wind has been scented. The wind blowing from the south is made to smell of olive oil (told you he was Italian) and the wind blowing from the north is made to smell of turpentine (perhaps he used to be a decorator). Pigeons then had drops of either olive oil or turps placed on their nostrils and they flew in the direction that they associated with that smell. However, there are few problems with this study, firstly it is thought pigeons have a poor sense of smell and it is not easy to replicate due to weather conditions. Honey bees also use smell to locate their own hive. Bees entering the wrong hive can cause ‘civil unrest’ with host bees fighting off the aliens.
Fishy smells Experiments have been carried out on salmon returning to their natal stream. Hasler (1986) found that plugging the nostrils of a salmon prevented it from accurately locating its own stream. Grier & Burk (1992) exposed young salmon to either one of two artificial smells in Lake Michigan. On their return to the lake they entered the stream matching that smell on 90% of occasions. It is not clear what smell the salmon are responding to under natural conditions. It could be a case of imprinting on the characteristic smell of that particular stream at a very young age or a response to pheromones released by their relatives. The most likely answer is both.
Navigation by direction This is the more sophisticated method of navigation and is necessary for homing or migrating over long distances. Possible methods available to species include use of sun, moon and stars and magnetic fields. Sun Humans have navigated using the sun for thousands of years and on clear days, even without any complex equipment it is possible to find directions from the position of the sun (east to west) in the sky. However, in order to do this we also need to know the time of day. For example we know that at midday, in the northern hemisphere, the sun is in the south and so on… Obviously we use clocks (the clock sold by Del Boy that made him a millionaire, was designed for navigational purposes at sea!), other species rely on their body clocks. Research evidence Bellrose (1958) noted that on clear days (when the sun is visible) mallards take off and immediately start heading in the right direction. However, on overcast days they appear disorientated at the start and fly randomly before finding their bearings.
Santschi (1911) used mirrors to reflect light from other directions and confused the movement of ants.
Polarised light This is light that has passed through a filter such as the Earth’s atmosphere. Depending on how high in the sky the sun is more or less polarised light gets through. When the sun is high in the sky (around midday) very little polarisation occurs. But just after sunrise and just before sunset lots of polarised light reaches the Earth’s surface. (See your local physicist for more detail). It is thought that some species, for example homing pigeons can detect polarised light and as a result can tell the position of the sun even on days when it is obscured by cloud cover.
Von Frisch
(ultimate anorak when it comes to bees, much more on him later when we do
communication) believes that bees use polarised light to indicate position
of nectar sources in relation to the hive. It is necessary for some blue
sky to be visible for this to be possible! He confused bees by passing UV
light through a filter (creating polarisation). This caused the bees to
alter the direction of their infamous bee dances!
Clock-shifting As I’ve already pointed out animals rely on their biological rhythms to navigate using the sun. These experiments are designed to alter the animals’ rhythms, confuse them into thinking it’s a different time of day, and observing what effect this has on their navigation. Walcott (1972) and Keeton (1974) altered the body clocks of seagulls and pigeons respectively. The birds are kept under artificial lighting, for example lights come on at midnight and go off at midday, about six hours earlier than the natural conditions outside. As a result when the birds are released their clocks are six hours out. This equates to 90 degrees of sun movement. As a result when the birds are transported away from their loft and released hundreds of miles away the set off in the wrong direction, e.g. heading north instead of east! However, they still find their way home eventually suggesting that the sun is used as a first resort, but that if this fails they have other methods that they can rely on.
How birds use the sun to navigate Two methods have been suggested. The map-compass hypothesis is the method already outlined above. Animals consider the position of the sun from east to west in the sky. So if they fly towards the sun in the evening they are going in a westerly direction etc. The sun-arc hypothesis is more complex because it suggests that species also consider the height of the sun in the sky. For this to work the bird etc. must learn the position of the sun (height and position east to west) for each time of day in its home location. When moved away from home it is able to determine where it is for example if the sun is lower in the sky than expected it realises that it is further north than home etc. Grier & Burk (1992) showed that birds only adjust for position east to west, not height of sun in the sky, suggesting that the simpler map-compass method is used. Stars Bellrose (1958) attached spotlights to the feet of mallards so he could track them at night. He found that when the sky was clear and the stars visible that the birds would all fly in the same direction. However, when the sky was overcast birds would fly aimlessly. In the Northern hemisphere it appears to be the Plough (or big Dipper for our American Cousins*) that is used as a direction finder. The Plough is adjacent to the Pole star and rotates around it. As a result it is always in the North.
Emlen (1975) highlighted the importance of the plough by rearing young buntings in a planetarium under an artificial night’s sky. In the wild the birds migrate south in autumn and return home, in a northerly direction, in the spring. In the planetarium the young birds appear to imprint on the Plough and fly away from this (South) in autumn and towards it (North) in the spring. Emlen placed ink pads and blotting paper around the bird’s cages to record their foot prints and gauge which way they were trying to fly. In a follow up experiment Emlen imprinted the birds on the star Betelgeuse (pronounced ‘beetlejuice) in the constellation of Orion. When the birds were released into the wild they flew in the opposite direction to the one expected. Crucially what this does show is that although birds appear to have an innate ability to imprint on stars for the purposes of navigation, there is still an element of learning involved. *Piece of trivia: President Abraham Lincoln was watching the play ‘Our American Cousin’ at the Ford Theatre in Washington DC when he was assassinated!
Magnetic fields
As we have seen birds may be temporarily disorientated by clock shifting and by overcast skies etc., but they seem to have a back up, fail safe mechanism for navigating if all other methods fail. Keeton (1969) and others have fitted magnets or Helmoltz coils (electromagnets) to the heads of birds such as pigeons or laughing gulls and found that they become disorientated. However, this only happened on overcast days when the position of the sun could not be judged. Their conclusion is that birds use the sun as their first choice but if this fails they use magnetic fields. Gould (1982) reported that pigeons can become disorientated by magnetic storms and there have been reported cases of many homing pigeons being lost when racing during such storms. Emlen (1976), in an experiment similar to his planetarium study, placed young buntings in cages in a shed. The shed had a large Helmoltz coil fitted to the roof. Using this, Emlen was able to vary the direction of the magnetic field inside the shed. In the spring young birds would normally jump in a Northerly direction mimicking their migration north. However, when Emlen adjusted the magnetic field by 120 degrees he found that the birds started to jump in a south easterly direction instead.
How animals detect magnetic fields The mechanism is not clearly understood. Beason (1989) found magnetite, a compound of iron, in the brain of a bird called the bobolink. When magnetic fields around the bobolink were altered using magnets, electrical activity was recorded in these brain areas. Others however, remain sceptical. Wiltscko & Wiltschko (1988) suggest that it may be possible for the Earth’s magnetic fields to be detected within the visual system of some species. As with animal memory, evaluation marks are tricky for this topic. Think of what the evidence suggests and emphasise that animals seem to use different techniques in different circumstances. Over long distances the sun appears to be the first choice for most species. However, at night this is obviously not possible so the stars are used (especially the Pole star and Plough). If conditions are overcast and sun and stars are not visible then at least some species appear to have the ability to use magnetic fields. Although these methods are good for covering long distances they are not precise enough to get an animal to its exact location. Having got close to their destination precise homing can be achieved using methods such as visual landmarks or smells or both. Other evaluation marks can be earned by considering the possible roles played by innate factors and learning and by criticising and/or comparing studies.
Loggerhead turtles If the thought of pigeons with magnets strapped to their heads sounded strange then look at what they did to the poor old turtles! Turtles hatch from their shells on the Florida coast and crawl to the sea. From there they migrate across the Atlantic Ocean in a clockwise direction, following a current known as the North Atlantic Gyre, swimming around the Sargasso sea. From Florida they head towards the Azores before heading south to the Canaries and finally back across the Atlantic to Florida. Lohmann (2001) believed that they inherited a built in migratory route which they were able to follow using magnetic fields. To test this hypothesis Lohmann fitted 79 baby turtles with a blue nylon-Lycra "bathing suit" that was tethered to a tracking system. The turtles were then placed in a shallow circular water tank. Surrounding the tank was a huge electric coil that generated magnetic fields. Lohmann's team exposed the turtles to magnetic fields that simulated three key locations along the migratory route—northern Florida, the north eastern gyre near Portugal, and the southern gyre—and recorded the direction in which each animal swam. "We found that turtles followed their migratory route," said Lohmann. When the turtles were exposed to a magnetic field that mimics the one that occurs near Portugal, for example, the turtles paddled south. In the ocean, the movement in that direction would keep the turtles in warm, nutrient-rich circuit and away from cold waters. In a second report published in Science, scientists have discovered a collection of nerve cells in the brains of subterranean Zambian mole rats that enable the animal to process magnetic information used in navigation. The mole rats dig tunnels up to 200 metres long and build their nests in the southernmost tip of their burrows. As the direction of the magnetic field changes, so does the location of the moles' nests. As in the loggerhead turtle study, the German and Czech researchers who conducted the mole rat study have not yet determined how the mole rats detect the magnetic fields.
How animals detect magnetic fields The mechanism is not clearly understood. Beason (1989) found magnetite, a compound of iron, in the brain of a bird called the bobolink. When magnetic fields around the bobolink were altered using magnets, electrical activity was recorded in these brain areas. Others however, remain sceptical. Wiltscko & Wiltschko (1988) suggest that it may be possible for the Earth’s magnetic fields to be detected within the visual system of some species. As with animal memory, evaluation marks are tricky for this topic. Think of what the evidence suggests and emphasise that animals seem to use different techniques in different circumstances. Over long distances the sun appears to be the first choice for most species. However, at night this is obviously not possible so the stars are used (especially the Pole star and Plough). If conditions are overcast and sun and stars are not visible then at least some species appear to have the ability to use magnetic fields. Although these methods are good for covering long distances they are not precise enough to get an animal to its exact location. Having got close to their destination precise homing can be achieved using methods such as visual landmarks or smells or both. Other evaluation marks can be earned by considering the possible roles played by innate factors and learning and by criticising and/or comparing studies.
Extension Possible mechanisms for detecting magnetic fields in marine animals This stuff gets a bit technical in places but I’ll try and explain it in simple terms
1. Electromagnetic induction When a current flows in a magnetic field it experiences a force at right angles to it. Not sure if you still do this in A-level physics but the direction of the force can be explained using ‘Fleming’s left hand rule.’ As the direction of the magnetic field changes so will the direction of the force on the current and it seems that some species such as rays and sharks are able to detect this very precisely. (Lohmann and Johnsen 2000). 2. Biogenic magnetite This is the system used by the bobolink (above). Crystals of magnetite (Fe2O4) have been found in various species. The precise mechanism seems to vary from species to species but it seems that these tiny microscopic crystals change their pattern of rotation depending on the direction of the Earth’s magnetic field. This change is then detected by filaments in certain cells that allow the animal to determine direction and possibly even strength of the field. This all sounds a little vague I know, but apart from my simplification of the theory, it also happens to be very new… (Johnsen and Lohmann 2005). The olfactory lamellae of trout (the bit it uses to detect smell) seem to contain these crystals, as does an area close to the olfactory nerve of the bobolink. It has been estimated that the bobolink can detect a change as small as 0.5% in the Earth’s magnetic field. It seems reasonable to assume that salmon have a similar mechanism. For more detail on these ideas see:
There is also a third possible mechanism outlined but that looked far too complex to even start deciphering into plain English!
Introduction All animals communicate, either with members of their own species or across species. Communication can act as a warning, a mating call or for a number of other purposes. However, does simple communication of this type constitute language? Hockett, and others have laid down criteria that distinguish language from mere communication, for example a true language is able to communicate ideas about events in the past or future, so called displacement. This section looks at:
What is communication? Put simply it is a two way process that allows a message to be sent and received. Obviously for the message to be useful to both sender and receiver, the signal sent must have the same meaning for both of them. Think of the confusion an Englishman in New York might cause by asking for a ‘fag!’ It also seems safe to assume that communication (or signalling) of this sort must confer some evolutionary advantage on species as a whole, otherwise it would not have survived as a pattern of behaviour. Individuals that use signals would have been more likely to survive and prosper and pass their genetic material into the next generation. However, there are examples when signals like these can be of disadvantage to either the sender or receiver. (see details on eaves dropping and dishonest signals). Some possible advantages of signals:
members of the species of an approaching predator. (Ververt monkey).
of members of the opposite sex. (Peacock's tail).
submissive signals that settle most disputes without recourse to physical aggression. (Arched back of a domestic cat).
of food locations. (Waggledance of the honeybee).
1. Honest signals These usually involve ritualised forms of normal gestures to provide a message with unmistakeable meaning. For example the cowering of a dog to represent submission or fear. Many mating signals also fit into this category. Ritualisation: Most honest signals are exaggerated forms of animal behaviour. For example the arching of a cat or dogs back to exaggerate its height is used as a sign of dominance to ward off would be aggressors. Similarly the cowering posture that reduces their size is used to signal an individual’s submissive nature. Used together these two signals can avoid costly and aggressive encounters. Ritualised signals tend to be highly conspicuous (and may involve lots of noise or elaborate movements). This ensures that the signals are noticed! They also tend to be very stereotyped ensuring that they are not misinterpreted. In some cases this can ensure that an animal does not waste its time (and all street cred’) by attempting to mate with the wrong species!!! 2.Dishonest signals These aim to deceive and put the receiver at a disadvantage. For example smaller male cricket frogs lower the tone of their croak to make themselves sound larger. (A ploy used by some men in male dominated industries to make themselves appear more macho!). The young cuckoo signalling hunger and deceiving its adoptive parent into giving it food. 3. Eaves-dropping When a predator picks up signals that are not meant for it. For example if a signal, intended to pick up a mate, is intercepted by a predator that then uses the information to locate the signaller. The female bark beetle (all life is here!), releases a scent to attract males to her tree. However, other females intercept the signal and close in on the sender and take advantage of the attracted males she is attracting!
Channels of communication This refers to the sensual (broadest sense) methods that a species can use, such as visual, auditory, tactile etc. Each has its advantages and disadvantages and below is a list of these with specific animal examples. Visual It is estimated that about 70% (some estimates put it higher) of human spoken language is actually conveyed visually in the form of body language. In the animal world visual messages are widely used in courtship especially in birds and fish. The male stickleback will perform ‘zig-zag’ dance that can stimulate a female into releasing her eggs into the water for the male to fertilise. Robins will attack red feathers nailed to a tree but will completely ignore a whole stuffed robin that does not possess red colouration (Lack 1943).
Channels of Communication
Auditory (sounds) As humans (speaking for the majority of us now), this is the channel we most associate with language and communication. Many other species, most notably birds, also make good use of sounds in communication and signalling. Sounds can be varied in a number of ways: · Pitch (or tone): female toads apparently prefer males with a deep ‘voice’ as they suggest larger males (obviously no one has told them that size doesn’t matter Ed). · Volume: clearly a louder signal will have more impact and travel further. · Sequence: the order in which the sounds are deployed, crucial in human language but also in other species such as crickets. Many species vary all three to good effect to alter the meaning of their call. A good example of this is the vervet monkey that we will look at in more detail later.
Olfactory (smells) Pheromones (chemical messengers) are usually the method of first choice! Releaser pheromones usually have a short term effect bringing about a sudden change in behaviour, for example attracting male moths to a female releaser. Primer pheromones usually have a longer term effect and may alter the physiology of the receiver. It is common for many species such as domestic cats to mark their territory with scent. This is achieved by the pheromones in their urine. A few statistics: each antenna of the male silk worm moth has 10,000 hairs that it uses to detect female pheromones. Just a few molecules can change the behaviour of the moth. Simmons (1990) found that smell can be crucial in preventing accidental incestuous breeding. Female crickets showed a preference for more unrelated males as evidenced by their pheromone. Attachments between mother and offspring may also be mediated by smell. Farmers will cover an orphaned lamb in the afterbirth of another newly born lamb to persuade the mother to adopt the orphan. (Once saw this being done… then went home and had a neck of lamb casserole that I’d made earlier!)
What is language? Psychologists as well as linguists have problems in defining ‘language,’ both finding it easier and more useful to identify the different properties that characterise language. The most widely used set of criteria are those devised by linguist Charles Hockett who has compared human languages with other forms of communication. Hockett’s criteria: Symbolic or semanticity: the method of communication uses symbols that have a shared meaning between all those members of the species using it. In human terms, the word ‘tree’ in English, has a shared meaning between all people around the world that speak our language. Syntax: the use of these symbols requires rules, for example in English the adjective usually goes before the noun ‘the red book’ as opposed to ‘the book red.’ Those that do French will be aware that this is not always the case in French. Some adjectives are placed after the noun. Arbitrariness: the symbols used bear no resemblance to the action or object that they are representing. The word ‘car’ is arbitrary since it looks or sounds nothing like the object that it represents. The waggledance of the bee however is not arbitrary since the direction of the dance represents the direction of the nectar and the speed of the dance reflects the distance. Specialisation: the sounds created have no other function other than what they are representing. For example the panting of a dog has a biological purpose. A dog squealing because of pain does not do so to communicate the pain but because it is in pain. Displacement: the language can communicate about actions, objects or emotions that are not present or visible at that moment. For example the waggledance shows displacement because it refers to nectar not visible to the dancer. Human languages can communicate ideas about actions that occurred yesterday or may happen tomorrow, so are not impinging on the individual at that moment. Most animal communication refers to immediate environmental stimuli such as the presence of a predator. Cultural transmission: the method of communication is passed from one generation to the next by a process of teaching. This appears to be the case with some birdsong but is not true of the waggledance which is innate and present from birth. Generativity or productivity: the number of utterances possible using the language is infinite. Using the English language I could say ‘Me and Kylie popped down the Sugarloaf for a pint of Abbot and a prawn vindaloo.’ The chances are nobody has ever said that before. Most methods of animal communication have nothing like that level of flexibility. The calls of most species are very limited in scope. Prevarication: the language can be used to tell lies or jokes. Discreteness: the language combines smaller units (e.g. words) to create meaning (e.g. sentences). Interchangeability: an individual can both send and receive messages. Hockett’s first criterion, not mentioned above, is that the language should be vocal or auditory. I leave this ‘til last since it not only rules out the waggledance, but would appear to relegate nearly all attempts of teaching apes and cetaceans to mere communication. It would also rule out sign language!!!
Does natural animal communication constitute language? What follows is a brief description of various natural signalling systems and a consideration of whether or not they fulfil Hockett's criteria. 1. Birds Birds make most use of the auditory channel, so called birdsong. This is often used in conjunction with other channels such as visual signalling. Hunter and Krebs (1979) found that the nature of their song relates to their environment. · In open spaces birds use a wider range of frequencies and repeat notes and sequences of sound faster. · In dense forests they use lower frequencies. Wiley & Richards (1978) attributed this to communication of the message with minimum distortion. In forests trees cause reverberations. Lower pitched sounds are less likely to be disrupted. In open spaces the greatest risk is from strong winds. High-pitched sounds, quickly repeated are less likely to be affected.
Is birdsong innate or learned? (Easy evaluation marks to be had here). Crickets reared in isolation (so they have never heard other crickets sing), still sing themselves. Obviously, crickets are not birds, but this suggests that their song is innate. However, higher species, such as sparrows, when reared in isolation between 8 and 90 days old, fail to pick up birdsong, suggesting that it is learned, or as it applies to Hockett, ‘culturally transmitted.’ Note. It is possible for birds reared like this to pick up the song of related species. The conclusion, therefore is, that the ability to sing is innate, the nature of their song is learned.
Is it language? No.
2. Honeybee The dances of the honeybee were studied by von Frisch over a period of many years. Two distinct types of dance were observed: 1. The Round dance. (Indicating nectar within an 80m radius). The returning bee dances in a circle, as the name suggests. The other bees then fly off and search nearby. This dance gives no indication of direction. 2. The Waggledance. (Indicating nectar more than 80m away). The returning bee performs a more elaborate dance that indicates approximate distance, and crucially direction.
The greater the energy expenditure the nearer the nectar is to the hive. Remember that the hive is dark inside so visibility is minimal. The observing bees therefore follow the dancer to assess direction and the dancer herself regurgitates some of the nectar as an additional clue. Subsequent research has backed up von Frisch’s early work on the complex nature of the dance. The method of communication has some degree of flexibility. For example the bees only dance on about 10% of occasions when the source they have found is particularly plentiful or if the find satisfies a particular need of the hive. The receivers don’t always act on the information. The Goulds sat in a boat in the middle of a lake and provided nectar to passing bees. These returned to the hive and performed the appropriate dance communicating the location of the find. However, the others did not act upon the information. The Goulds assumed this was due to the bees having a mental or cognitive map of their immediate environment. They would have realised that the dance was indicating the presence of nectar in the middle of water. Since this would normally be impossible the receivers assume a mistake has been made and ignore the message.
Is it language? No. Additional points Bee dances are not productive in that the message is always communicating the same thing, no new subjects are incorporated. Also the language does not demonstrate reflexive in that the bees are unable to communicate anything about themselves.
3. Whales Whales communicate via song and this is often compared to the songs of birds. Typically a song lasts about 30 minutes and comprises long, slow notes. Songs are split into themes and themes into phrases. Finally each phrase comprises notes. Whale species average about six themes, but they do change over time. All the whales in a given area sing the same song but this does change during the course of a season. At the start of the next singing season the whales sing the same song as they were singing at the end of the previous season. The meaning of the songs is difficult to interpret and a number of suggestions have been put forward. Some have suggested that given the huge brain of the whale its songs must have complex meanings, but this appears not to be the case. 1. Mating call. Winn & Winn (1985), along with others, have reported that only males sing suggesting a mating role for the songs, seeking to attract females. They suggest that a build up of androgen (male hormone) triggers the call. Tyack (1981) watched singers pursue non singers and then engage in courtship type behaviour, again suggesting a mating role. 2. Warding off other males. Winn & Winn (1985) suggest that the lower frequency notes of the songs may be an attempt by males to keep other males at bay. Typically songs combine notes of different pitch, so the songs could be conveying different messages. 3. Feeding behaviour. (D’Vincent 1985) suggest songs appear to play a vital role in all manner of social behaviours including feeding. 4. Surfacing. Whales need to surface at regular intervals, Winn et al (1979) report a ‘ratcheting sound’ immediately prior to surfacing and this has enabled scientists to predict when whales will surface.
Is it language? No.
4. Ververt monkey Signals appear to communicate the presence of danger and the most appropriate means of escape. Seyfarth & Cheney (1980) carried out a field study of their signals. Three main ones are evident: · High pitched, indicating snake and causing other monkeys to stand upright. · Loud bark, indicating presence of a leopard and results in others climbing trees. · Chuckle, indicating eagle overhead and resulting in others heading for bushes. Seyfarth & Cheney (1980) recorded the calls and played them back in the absence of predators. The ververts still reacted suggesting that the song per se, rather than a visual threat causes the response.
Is it language? No. Other points on monkey communication Vervet communication has few meanings so does not demonstrate generativity (or productivity). Reflexivity (the ability to communicate about oneself) does not appear to be present and there is no evidence of ‘duality of patterning’ or discreteness, in which small units of language are combined to form more complex meanings. The only way the ververt could conceivably do this is presumably by warning others of eagles and leopards at the same time!
5. Chimpanzees Chimps communicate using a combination of auditory signals accompanied by visual messages, particularly movements and gestures. Grunts: For example soft grunts are produced at times of feeding and grooming and appear to be linked to contentment. Pan grunts: These are grunts separated by audible breathing and usually signify the approach of another chimpanzee. Pant hoots: reported by van Lawick-Goodall (1976). These are a series of ‘hooo’ sounds, again joined by audible intakes of breath. Think of Cheetah from the television series Daktari! These increase in volume and are associated with excitement. Other sounds in the chimp repertoire include squarks, whispers and barking. Each sound is accompanied by various facial expressi Do animals naturally possess language? Most researchers in the area believe that real language does not occur naturally in non-human species. This runs counter to the theories of Skinner but supports the views of Chomsky. Chomsky believed that humans possess a Language Acquisition Device (LAD) that predisposes us to learn a language. No other species has this, according to the great man. The LAD seems to lay down in our brains the basis for acquiring the elements of language such as syntax. The language that we learn is determined by our environment and by our experience, be it English, Greek or Swahili. However, the fact that we are able to acquire language is genetically determined. Having concluded that non-human animals do not possess language, can they be taught? More to the point, why bother? Apart from being fun, it is an attempt to resolve a long running philosophical argument between Chomsky and Skinner.
Teaching human language to non-human animals Early attempts failed since researchers tried to get chimpanzees to talk. Unfortunately they do not have the necessary vocal equipment to do this Gua Kellogg & Kellogg (1933) reared her with their own child. Gua learned to say three words. Viki Hayes & Hayes taught her to speak four words, ‘papa,’ ‘mama,’ ‘up’ and ‘cup.’ However, she was unable to use these in the correct context! Washoe Was taught American Sign Language (ASL or Ameslan) by Gardner & Gardner. They used modelling, making the appropriate sign themselves and reinforcing Washoe’s behaviour if she copied. This is very much in line with the behaviourist approach and in keeping with the way that Skinner himself believed that we acquire language. If this method failed the Gardners would physically shape Washoe’s hands into the correct sign.
Evaluation * However, Terrace et al (1979) argued that she was simply describing the two things she saw, i.e. some water and a bird, rather than attempting to combine the two. * There is famous footage of Washoe supposedly using language. In this it does appear that she is simply imitating the signs made by the Gardners. * Also many of the signs produced by Washoe are the same as signs produced by chimps in the wild. In which case it can be argued that the signs are not symbolic, one of the criteria for language. Nim Chimsky Rather amusingly, according to all the text books, named after Noam Chomsky. After five years Nim had learned many signs but according to Terrace showed no sign of grammatical structure, which like Chomsky, he believed to be crucial for language. Terrace believed that Nim was simply learning by stimulus response and making no real attempt to use the signs to communicate. On the face of it Nim’s achievements were significant. In one 18 month period he signed over 19,000 multi-word phrases. However, when Terrace analysed the signing by counting the mean length of utterance (mlu), i.e. how many words were being used in a phrase, he discovered this to be 1.5. Nim’s phrases were limited to one or two words only. Regardless of the amount of training received, Nim failed to produce longer sentences. Nim died in 2000.
Evaluation * Terrace used a number of different volunteers to work with Nim. Some of these may not have been trained properly. * The most likely reason for Nim’s supposedly poor performance compared to other chimps is that Terrace was particularly careful to distinguish ‘language’ from mere imitation. * Terrace argued that the way in which chimps and human children acquire language is fundamentally different. According to Terrace chimps learn language by conditioning or stimulus-response learning, much as Skinner had predicted. As a result they appear not to use language for pleasure or creatively as humans do. Was Nim’s language qualitatively different to humans i.e. was it so far removed from human language as not to be considered language at all, or was it merely quantitatively different i.e. language but simply not as complex?
The Oklahoma colony The apparent problems with the Washoe study and others that had gone before, could have been due to lack of knowledge by the trainers. Neither the Gardners, nor Terrace had been fluent users of AMESLAN before the trials started. Another potential problem was that the chimps had been raised in isolation so had had no opportunity to use their language with others of their own species. Researchers had no idea whether or not chimps, having acquired the sign language, would then use it to communicate with other chimps. The Oklahoma colony was set up by Fouts to resolve both of these issues. The chimps were reared together as a colony and taught to use AMESLAN by people who had used it themselves since childhood. Findings: The chimps did appear to use the sign language to communicate with one another when their trainers were not around. Fouts carried out an experiment in which one of the chimps was shown the location of some hidden food before returning the chimp to the colony. The other chimps would then search for the food in the correct place suggesting that the first chimp had communicated the information to the others. Lucy, who was mentioned in the video, was given a four day old radish that must have been particularly ‘hot.’ She described the radish as ‘hurt-cry-fruit.’ Lucy did provide other evidence for the creative use of language when she described a water melon as ‘candy-drink’ or fruit-drink.’ Koko Two gorillas, Koko and Michael took part in Project Koko, an attempt to teach AMESLAN to gorillas. The researchers claim that Koko has the most extensive vocabulary of any non-human. Koko has a working vocabulary of over 1,000 signs and can understand about 2,000 words of spoken English. The Pattersons claim that Koko is able to combine words to create new meaning for example on seeing a zebra she signed ‘white tiger.’ An example of displacement was her apology for biting someone three days earlier. However, her communications are brief and have not shown significant increases in mlu over time as would be expected, for example with a human infant.
Sarah Premack & Premack (1972) taught Sarah to communicate using plastic symbols on a magnetic board. By the end of her training she could construct two or three word ‘sentences’ involving nouns, verbs and adjectives. However, she did not grasp word order, but this is not crucial for true language. Apparently word order is not vital in some human languages, for example Finnish. Yerkes colony in Atlanta Lana Rumbaugh (1977) taught Lana to use a lexigram. This uses a large adapted keyboard to display symbols on a computer screen. These symbols are arbitrary representations of objects etc. The keyboard is connected to a voice synthesiser so that when the keys are depressed the corresponding word is produced audibly in sound. The keyboard language is referred to as ‘Yerkish.’ It is claimed that Lana could distinguish word order, for example the difference between ‘Tim give Lana apple’ and ‘Lana give Tim apple.’ She was also able to generate symbols for objects for which she did not know the symbols. For example on seeing a cucumber, she put up the symbols for ‘a banana that is green.’ This seems to provide evidence for generativity or production. Later, having got married, Savage-Rumbaugh, criticised the earlier work of Terrace and others for concentrating on production of language rather than on comprehension. This seems to be a valid point when you consider how humans learn language, understanding words before being able to reproduce them. Pygmy chimpanzees (bonobos). The first attempts to teach bonobos were made on a chimp called Matata. She was born in the wild and didn’t start her lexigram training until the age of five. In total she learned only 8 symbols. However, Matata had kidnapped a young bonobo, called Kanzi, from its real mother and was rearing him as her own. Between the ages of 6 months and 2 and a half years Kanzi watched as the trainers worked on teaching Matata the use of the lexigram. During this time no attempts were made to formally teach Kanzi and he showed little interest in what Matata was being taught. Following the disappointing results with Matata the experimenters believed that bonobos were not suitable candidates for acquiring language. Despite this, when Kanzi was 2 ½ years old the Savage-Rumbaughs decided to introduce Kanzi to the lexigram, only to discover that he could already use it. He had apparently learned indirectly by watching Matata. In follow up trials he was never taught directly and was never rewarded for correct usage. Instead he learned by watching others use it. Kanzi eventually learned 150 symbols and demonstrated excellent comprehension and was able to respond appropriately to 105 action-object pairings, for example ‘get the orange from the colony room’ or ‘Kanzi get me a knife.’ However, as with Nim, his mlu showed no increase over time as it would have done with a human child. Most of his utterances continued to consist of only one symbol (an mlu of one!). In some of the studies Kanzi listens to a stranger on the telephone asking him questions and he has to reply via the lexigram in Yerkish. This is an example of double-blind testing since it removes nearly all possibility of experimenter bias. In one exchange the voice asked Kanzi what he wanted and he replied ‘M & Ms’ on the keyboard In 1993 the Savage-Rumbaughs compared Kanzi (aged 9) with Alia, a two year old child who had been taught to use the lexigram. Both were tested on over 400 sentences. * Kanzi was right on 74% of occasions * Alia was right on 65% of occasions. It is essential to mention that the way Kanzi acquired ‘language’ is similar to how humans, as infants learn to speak. Rather than being formally taught, we pick up the basics of language by listening to others. Another excellent evaluation point is to consider why the attempt to teach Matata was so unsuccessful. Not only was she taught formally, she was also five years old when training began. This provides evidence for the idea of a critical period in language development. If language is introduced after the critical period then it is too late to pick it up. (Think of the example of Genie from year 12).
Panbanisha The Yerkes colony now has another bonobo, called Panbanisha. It is claimed that she is able to express a sense of humour through her language training. She watched a person replace sweets in a sweet box with insects. When a second person went to open the box and asked Panbanisha what was inside, she replied ‘sweets.’ Realising that the second person was being tricked she added that the first person was being ‘bad.’ Dolphins Due to their intelligence and brain size, dolphins seem to be an obvious species to teach. Lilly (1965) taught dolphins to mimic human sounds and sing songs, for example ‘Happy birthday.’ This was done by operant conditioning, in the same way as they’re taught to jump through hoops. Mimicry of this sort however is far removed from language as we know it. Later attempts were made to teach them understanding of language based on the movement and gestures of their handlers. Herman et al (1980) worked with two bottlenose dolphins Akeakamai and Phoenix. They could be taught quite complex instructions usually involving fetching and moving of objects. Phoenix was taught to obey computer-generated sounds and Akeakamai was taught to respond to gestures. In both cases the symbols are arbitrary in that they bear no resemblance to the object that they represent. To ensure against unintentional cues the handlers wear dark glasses and different researchers conduct the studies. The researchers claim clear signs of syntax since the order of the symbols is crucial to the understanding of the instructions. Words are classed as either object, object modifier or an action. In the case of Ake (has she is known to her friends), the gesture ‘BALL HOOP FETCH’ However, the dolphins are unable to communicate back to their human handlers or to use the methods that they’ve learned to communicate with other dolphins. Research on dolphins is still in its infancy compared to primate research, so at present more work is needed.
Concluding comments * In the wild chimpanzees communicate with a combination of sounds, gestures and facial expressions. Teaching them to use language based on signs is therefore very unnatural. The version of ASL used is particularly artificial. * Many of the apes meet most of Hockett’s criteria; however, evidence for some of these is minimal. Their use of semantics is limited and there is little evidence of displacement or generativity (production). * Some chimps have shown definite signs of displacement and limited prevarication. In some experiments either food or a threatening object such as a plastic snake are hidden so that only one chimp knows the location. In the case of food the chimp will not tell the others the location, but will eat the food himself when the others have gone. In the case of the snake the chimp gets very ‘agitated’ when the others go near it. * There is evidence from brain scans that chimps may have the potential for language. The human brain has structures in the left hemisphere related to language (e.g. Brocas and Wernickes). Similar structures have been found in the left hemispheres of chimps. * The ability of apes in comparison to children falls short in a number of ways: a. It is rare for apes to use language spontaneously, i.e. without being asked to. b. The mlu of apes falls well short of that of children. c. Apes rarely show signs of displacement, communicating mostly about objects that are present rather than objects out of sight, or ones that have not been seen for some time. Chomsky sums it up nicely when he suggests that apes having the ability to use language but not using it are like birds having wings but never bothering to fly! At best the evidence to date offers weak support for the continuity argument as proposed by Skinner, with animals having the ability for language, but just not as sophisticated as humans. At worst it seems to provide evidence for the discontinuity theory, the vocabulary being used in such a poor way as not to constitute language at all. If the discontinuity theory, as proposed by Chomsky, is correct, then language stands alone as the one behaviour separating humans from all other non-human species!
Introduction
A few, apparently obvious points are worth making at the outset:
Practicalities of setting questions on this topic:
This is a short topic. When compared to some of the others, ridiculously so (need I remind you of Piaget etc.). As a result questions are limited. Looking at suggested questions (as yet there are no real past questions to go on), questions may be split to cover two different areas of the topic, for example:
Areas covered by these notes: Explanations of spatial memory (spatial adaptation and pliancy models) Use of memory in foraging and food caching Use of memory in navigation Cognitive maps and neurological bases of memory
Areas to cover when answering questions:
Spatial memory and Navigation We know that some species have an amazing capacity for navigation, for example salmon, pigeons etc. The ability to remember locations is highly adaptive (i.e. will add to the animals survival and reproductive ability), since it will enable the animal to find its way home to ‘the wife and kids’, to remember feeding grounds’ locations where potential predators hang out and locations of possible mates (and I don’t mean the sort you take for a beer!). Spatial memory appears to develop early in life. Regolin & Rose (1999) taught two day old chicks to find other chicks by successfully avoiding a barrier. The chicks were able to remember this task 24 hours later. As we have seen in navigation, many species appear to use landmarks in finding home locations.
Gould (1987) suggested that one of two possible methods could be used.
Gould (1986) provided evidence for mental representations in his beloved bees! We have already seen his experiment with the boat in the lake that suggests that honeybees use mental representations in finding nectar, this was reinforced using the following procedure. Bees are taught to fly to a point (A) to find food. They were then transported to different point (B) in a dark container and released. They were still able to fly directly to point A, even though they were presumably unaware of their displacement. Gould believes that before the experiment the bees had formed a cognitive map of their environment. Baerends (1941) provided evidence for the simple method. He noticed that wasps used landmarks close to and distant from the nest. Using these they were able to navigate different routes home, however, they never seemed to combine routes suggesting that each route had been memorised separately. Tinbergen (1951) provided some evidence for the more complex method by placing a triangle of cones over the nest. Nearby he placed a triangle of stones. On their return the wasps returned to the triangle of stones. Tinbergen concluded that the wasps were using spatial relationships rather than precise visual cues (i.e. patterns in the environment rather than distinct objects). Time permitting in an essay you could also comment that Tinbergen & Kruyt ruled out the use of smell by using a combination of pine-scented cones and pine-scented plates. It was clearly visual rather than olfactory clues that were being used. Having concluded that spatial memory does indeed exist the question remains what method of spatial memory do animals use. There are two main theories and this could be the basis of an examination question.
Models of Spatial memory The two models to be considered are similar but subtly different.
Spatial adaptation theory This assumes that if a species requires a good spatial memory then it will be at an evolutionary advantage to evolve one. So for example, if a species has to go out hunting over wide areas or if possible mates tend to meet at the watering whole at certain times only then the species will be at an advantage if it can find these locations without difficulty. Sherry et al (1992) believed that there was a correlation between living in an environment that is spatially demanding and having a good spatial ability. Gaulin & Fitzgerald (1989) have evidence for the model. Male meadow moles have a territory four times the size of the females. However, male prairie voles have a territory of similar size to that of the female. It would therefore be expected, if the spatial adaptation model is correct, that male meadow moles would have a better spatial ability than male prairie voles, simply because the meadow moles need it! When tested on a maze running task this is exactly what the researchers found.
Pliancy model Day et al (1999) however, suggested an alternative explanation for the meadow moles superior performance. Rather than having evolved a better spatial memory per se, Day believed that the animals had developed a more flexible (pliant) memory that it could adapt top whatever situation it found itself in. Day et al (1999) provided evidence for this alternative theory. A word of caution, this is a simple experiment but benefits from a few read-throughs. They compared two species of lizard, both with ridiculously long Latin names, so for the sake of your sanity I shall refer to them as AB and AS.
Be careful not to make the same assumption as me. On the face of it you would expect AS to need the better spatial ability but this is not the case! AS can sit and wait for its prey to pass by. On the other hand AB has to go out looking for it, so in fact it is AB that needs the better spatial memory, if the spatial adaptation theory is correct. In fact when Day et al tested the two species on a maze task there was no difference in spatial ability between the two species, suggesting that the spatial adaptation theory does not fit. However, when the two species were tested on a non-spatial task in which they had to choose whether to eat a worm, based on the colour of the background, AB did perform significantly faster. The researchers concluded that species that have to go out looking for food have better memories for ‘complex associations’ indicating a more flexible (pliant) memory, as opposed to a specific better spatial memory. This allows them to make faster decisions in changing or novel environments. To conclude an essay on navigation or spatial memory you could discuss the neurological bases of memory. See later notes for this.
Memory and food location and caching It is clearly advantageous for an animal to be able to remember locations where food is plentiful. There may also be occasions when food is so plentiful that there is too much to eat at that time so the only option is to store some of it for use on a ‘rainy day.’ In this case the animal must again be able to locate this cache of food.
Memorising food locations Two experiments demonstrate this ability: Menzel (1971): chimpanzees. The chimps were taken on a very circuitous route indoors. Outside they could see 18 food locations. When released outside they visited all 18 sites however, were able to take the shortest route between them. In a follow up study the experiment was repeated but this time 9 of the locations contained fruit and the other 9 vegetables. You may have guessed that chimps generally prefer fruit, so when released outside they visited the fruit sites first! This suggests that the chimps were able to build up an internal mental representation (or cognitive map) of their environment and make a bee-line for these favoured sites! More on this later.
Srinivasan et al (1997): bees. The bees were placed in a 3.2m long tunnel that had black and white vertical stripes painted down the walls. When they were moved to an identical tunnel but without food the bees flew back and forth eventually homing in on where the food should have been. Even when the number of stripes was altered the bees could still perform the task suggesting that the stripes were not being used as landmarks. However, when the stripes were altered so that they ran horizontally the bees were confused. The researchers concluded that the vertical stripes had been used as a measure of distance indicating ‘how much of the World was passing by.’
Memorising food cache locations Given a choice of food locations or food caches plump for this one since there is more research to discuss. It may be thought that a squirrels ability to find hidden nuts depends more upon its sense of smell than on its memory, but research by Jacobs & Liman (1991) suggests that this is not the case. Grey squirrels were allowed to bury ten hazelnuts in an area of 45 square metres. The nuts were later removed. Twelve days later the squirrels were released back into the area. It was found that the squirrels were far more likely to visit sites where they had buried nuts rather than sites were other squirrels had buried theirs, even though during the search they would have passed by and presumably smelt other squirrels’ nuts, (no jokes please!) Sherry (1984) investigated the memory of the black-capped chickadee, a bird species native to America that secretes hundreds of seeds in nark and moss. Sherry had 72 holes drilled into the bark of a tree and allowed the chickadees to hide five sunflower seeds in these holes. The nuts were removed and all 72 holes covered with Velcro. The birds were released 24 hours later and spent most of their time pecking at the sites where they had hidden their seeds. Again this suggests that it was solely memory rather than visual or olfactory clues that were being used to locate caches. Many species such as the chickadee seem to remember food cache sites for a limited period only. In the case of the chickadee memory seems to fade after 28 days. Reasons for this could be that food will deteriorate after this time or that chances are other animals would have found it. Either way it does suggest a possible evolutionary advantage to forgetting, a phenomenon we usually regard as problematic! However, other species such as the Clark’s nutcracker seem to have memories for food caches that last substantially longer, up to 40 weeks (Balda & Kamil 1992). In the wild this species bury more than 30,000 seeds, typically hiding about 4 seeds in each cache. Van der Wall (1982) estimated that a bird would need to memorise about 3,000 cache locations. The use of visual and olfactory cues to aid memory has not been ruled out.
Research on the brains of species that cache food show that they have more neurons (nerve cells) in an area of the brain called the hippocampus. (See later notes on neurological bases of spatial memory). Smulders (1995) reported that the enlargement in the hippocampus is particularly noticeable in Autumn when the birds are caching food for winter storage.
Cognitive Maps These are best discussed in an essay on memory in food location and caching but could be adapted for an essay on navigation. Cognitive maps were first discussed by Tolman (1948) who described them as internal, mental representations of ‘spatial relationships within the environment.’ Early explanations of a rat’s ability to run a maze involved operant conditioning, however, it was subsequently found that rats could learn mazes in the absence of reinforcement. Evidence for cognitive maps is provided by radial arm maze studies and detour studies.
Radial arm maze studies A typical radial arm maze comprises eight arms radiating out from a central point. Rats placed in such a maze will very quickly be able to locate food. They visit each arm in turn but not in any systematic way. Even so they do not visit the same arm twice. It seems as though they build up a mental image of their new environment and are able to orientate themselves using this. However, if the maze is made more complex by for example subdividing each arm into three other arms then a different strategy has to be employed. Rats do now employ a systematic method to explore, for example as we would do, always turning right on exiting an arm etc. Roberts (1979) believes that this is because the more complex mazes exceed the capacity of the rats’ cognitive maps.
Detour studies The basic procedure is to show an animal a goal (for example source of food) and then remove them via a circuitous route; the assumption being that if the animal can take a direct route to the food it must possess a cognitive map. The first evidence was provided by Koehler (1925) using dogs. However, he did not consider the possible previous knowledge of the dog so it is possible the dogs may have learned by trial and error. Later studies have been better controlled. For example Chapuis & Scardigli (1993) placed hamsters in a circular maze with lots of doors. During the training period doors were locked so the hamsters had to take the long way round to reach food. When on subsequent trials the doors were opened the hamsters were able to take short cuts.
Rats placed in a complex maze with lots of dead ends can quickly learn to locate food. If a blind alley is opened up allowing a short cut to the food rats will very quickly realise this and use the new route. This suggests that the rats are able to visualise the location of the food in relation to the entrance to the ma Cognitive maps have not been discovered in all species. Similar studies on chickens for example resulted in the bird brains only managing short cuts when they accidentally broke down barriers placed in their way!
Neurological basis of spatial memory and cognitive maps This section is included by way of extension material. However, the information contained within is not that difficult to get your head round so have a go. This will provide useful evaluation material! Background If you cast your minds back to AS I told you about the case of H.M. (Henry) who had severe, life threatening epilepsy. To alleviate his condition surgeons removed an area of his temporal lobes, (an area of the brain at the side of your head near your ears). At the time the brian was more poorly understood than it is today and the function of this area wasn’t precisely known. The temporal lobes contain a structure called the hippocampus (Latin for seahorse) which we now know is implicated in human memory. As a result H.M. is unable to lay down new memories, his condition being similar to that of Clive Wearing. It seems that the hippocampus is crucial in the spatial ability of animals.
Evidence for role of hippocampus Morris et al (1982) compared two groups of rats on a spatial learning task. The control group were ‘normal’ rats whilst the experimental group had lesions (damage) to their hippocampus. The rats were placed in water muddied by milk powder. Hidden beneath the water’s surface was a platform that the rats could stand on. Both groups were placed in the water and swam randomly until by chance they found the platform. In the follow up trial rats were placed back in the water and this time the ‘normal’ rats swam straight to the platform having remembered its location. The rats with damage to the hippocampus however, continued to swim randomly, just as they had done the first time. Morris concluded that the hippocampus must be involved in spatial memory. Bingman & Mench (1990) found that pigeons with damage to the hippocampus can navigate in the early stages of their homing i.e. when using stars, sun, magnetic fields etc. However, they could not find their way home to their own loft. That is they can find their way to the right area but not to a precise location. It is in these latter stages of navigation that the pigeons rely on their cognitive maps and the mental image of landmarks etc. needed to locate their own loft. Damage to the hippocampus therefore impairs the cognitive map but leaves other forms of navigation intact. Renkamper et al (1988) found that homing pigeons have a larger hippocampus than other pigeons. Smulders et al (1995) reported that the black capped chickadee has an enlarged hippocampus in the late autumn when the birds are caching food for the winter months.
Place cells of the hippocampus These are a group of cells that seem to become active in animals involved in spatial tasks.
Neurotransmitters in spatial memory If the neurotransmitter acetyl-choline is blocked in rats by administering the drug scopolamine spatial learning is impaired. Nilsson (1987) found that damaging acetyl-choline producing cells in the hippocampus impaired a rats performance on spatial learning tasks. However, if new acetyl-choline producing cells were injected impairments were reduced.
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